Hydrodealkylation process with promoted group vib metals and promoters

ABSTRACT

A process for the hydrodealkylation of alkyl-substituted aromatic hydrocarbons, including contacting the alkyl-substituted aromatic hydrocarbons with a catalyst comprising a metal of Group VIB of the Periodic System, such as chromium, molybdenum, and tungsten, and mixtures thereof, in an amount of about 5 to 15 per cent by weight of the finished catalyst, and a promoter selected from the group consisting of alkali metals, alkaline earth metals, rare earth metals, and mixtures thereof, such as potassium, rubidium, cesium, calcium, strontium, barium, cerium, thorium, etc., in an amount between about 1 to 10 percent by weight of the finished catalyst, at a temperature of about 1,050* to 1,200*F, a pressure of about 100 to 1,000 psig., a liquid hourly space velocity of about 0.1 to 5, and a hydrogento-hydrocarbon mole ratio between about 3 and 15 to 1.

United States Patent 1 Patrick et al.

[451 Sept. 18, 1973 HYDRODEALKYLATION PROCESS WITH PROMOTED GROUP VIBMETALS AND PROMOTERS [75] Inventors: Ralph E. Patrick, Flatwoods; RonaldA. Kmecak; Stephen M. Kovach, both of Ashland, all of Ky.

[73] Assignee: Ashland Oil, Inc., Ashland, Ky.

[22] Filed: Apr. 26, 1971 [21] App]. No.: 137,666

Related (1.8. Application Data [63] Continuation of Ser. No. 769,735,Oct. 22, 1968,

abandoned.

[521 US. Cl. 260/672 R, 208/112, 208/136,

I 252/462, 252/465 [51] Int. Cl B0lj 11/06, C07c 3/58 [58] Field ofSearch 260/672 R [56] References Cited UNITED STATES PATENTS 2,958,64311/1960 Friedman 208/60 2,858,348 10/1958 Bosmajian et al. 260/6682,895,905 7/1959 Kimberlin 208/137 3,193,592 7/1965 Eubank 260/6722,963,518 12/1960 Amos 260/672 Mason 260/668 Doumani 260/672 [57]ABSTRACT A process for the hydrodealkylation of alkylsubstitutedaromatic hydrocarbons, including contactingthe alkyl-substitutedaromatic hydrocarbons with a catalyst comprising a metal of Group VlB ofthe Periodic System, such as chromium, molybdenum, and tungsten, andmixtures thereof, in an amount of about 5 to 15 per cent by weight ofthe finished catalyst, and a promoter selected from the group consistingof alkali metals, alkaline earth metals, rare earth metals, and mixturesthereof, such as potassium, rubidium, cesium, calcium, strontium,barium, cerium, thorium, etc., in an amount between about 1 to 10percent by weight of the finished catalyst, at a temperature of about1,050 to 1,200F, a pressure of about 100 to 1,000 psig., a liquid hourlyspace velocity of about 0.1 to 5, and a hydrogen-to-hydrocarbon moleratio between about 3 and 15 to l.

8 Claims, No Drawings 1 HYDRODEALKYLATION PROCESS WITH PROMOTED GROUPVIB METALS AND PROMOTERS RELATED APPLICATIONS The present application isa continuation of Ser. No. 769,735, filed Oct. 22, 1968, now abandoned.Other related applications are Ser. No. 769,729, filed Oct. 22, 1968,now U.S. Pat. No. 3,700,745 and Ser. No. 769,733, filed Oct. 22, 1968,now U.S. Pat. No. 3,679,768.

BACKGROUND OF THE INVENTION The present invention relates to a processfor the hydrodealkylation of alkyl aromatics to the present aromatichydrocarbons. More specifically, the present invention relates to aprocess for the hydrodealkylation of alkyl aromatic hydrocarbons to theparent aromatic hydrocarbons, utilizing a unique catalyst system.

The hydrodealkylation of alkyl aromatics has been practiced for manyyears. The principal processes involve the conversion of toluene andlike alkylsubstituted benzenes to benzene, and coal tar light oils andcoal tar methyl naphthalene to benzene and naphthalene, respectively.These processes may be catalytic or non-catalytic in nature. Thenon-catalytic system which involves thermal dealkylation, in thepresence of hydrogen, requires high temperatures and pressures.

While the catalytic processes require lower temperatures and pressures,these temperatures and pressures are still quite high and thereforeresult in short catalyst life. Most commerical catalytic processesemploy chromia-magnesia deposited on an alumina base as a catalyst Sincethe development of this catalyst, there has really been no improvementin catalysts for this reaction.

It is therefore an object of the present invention to provide a newprocess for the hydrodealkylation of alkyl aromatic employing a novelcatalyst system. In a more specific aspect, the present inventionrelates to a process, for the hydrodealkylation of alkyl aromaticswherein catalysts which improve conversion are em-' ployed. Another and.further object of the present invention is to provide a process for thehydrodealkylation of aromatics wherein catalysts of higher selectivityare utilized. A still further object of the present invention is toprovide an improved process for the hydrodealkylation of alkyl aromaticswherein catalysts which reduce carbon lay-down on the catalyst areemployed. A further object of the present invention is to provide animproved hydrodealkylation process for the hydrodealkylation of alkylaromatics wherein novel catalysts are employed which permit operation atlower than conventional temperatures. Another and further object of thepresent invention is to provide an improved system for thehydrodealkylation of alkyl aromatics wherein-catalysts are employedwhich permit the use of lower hydrogen partial pressures.

SUMMARY OF THE INVENTION Briefly, in accordance with the presentinvention, alkyl aromatics are hydrodealkylated to their parent aromatichydrocarbons by contacting the alkyl aromatic with a catalyst comprisinga Group VIB metal oxide and an oxide selected from the group consistingof an alkali metal, an alkaline earth metal and a rare earth metal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Suitable feedstocks for use inaccordance with the present invention include toluene, polymethylbenzenes, coal tar light oils, coal tar methylnaphthalene concentrates,and bicyclic concentrates from light cycle oils and heavy reformates.Feedstock preparation includes fractionation to remove front ends orbottoms to thereby remove undesired fractions such as unsaturates,indanes and resinous materials. For example, it hasbeen found the coaltar'methylnaphthalene concentrates, as received from the coke oven,contain a large amount of contaminants, such as polymers, resins andfree carbon. Distillation of such raw materials to yield a percentoverhead leaves these materials as a bottoms. Hydrogenation andhydrotreating of the overhead fraction removes sulfur, nitrogen andoxygen contaminants, but, due to the thermal instability of thefeedstocks, a heavy resinous material is produced through thermalpolymerization. Distillation of the hydrotreated product is required toremove these resins and thereby reduce carbon lay-down on 1 thehydrodealkylation catalyst and reduce hydrogen consumption due tohydrocracking of the resins and polymers.

The processing conditions for the hydrodealkylation reaction of thepresent invention include a temperature between about l,050 and l,200F,a pressure between about and 1,000 psig., a liquid hourly space velocitybetween about 0.1 and 5, and a hydrogen-tohydrocarbon mole ratio ofabout 3 to 15/1.

The catalysts to be employed in accordance with the present inventioninclude metal oxides from Group VIB of the Periodic System, particularlychromium, molybdenum and tungsten. The promoters include alkali metaloxides of Group I of the Periodic System and, alkaline earth metaloxides of Group II of the Periodic System and the rare earth metals.Examples of materials of this nature which may be employed includepotassium, rubidium, and cesium; magnesium, calcium and strontium, andcerium and thorium, etc. The active metal and the promoter are depositedon an inert oxide support, which preferably includes a high area aluminahaving a boehmite, bayerite, beta, or eta crystalline form, or otheraluminas, silica-alumina, silica, silicamagnesia, silica-zirconia,alumina-magnesia, etc.

The optimum active metal content of the catalyst is about 5 to 15percent by weight based on'the final catalyst. The metal oxide promotershould be present in amounts of about 1 to 10 percent by weight.

The catalysts of the present invention may be prepared by well-knowntechniques in the art. Typical examples are coprecipitation orimpregnation techniques. One may employ extrudates or pellets forimpregnation or powders followed by pelletization or extrusion to yieldthe finished catalyst. The active metal and the promoter may be addedthrough the use of water- Example I.

To 200 ml. of distilled water was added 15 g. of cesium nitrate and 40g. of chromic acid. This solution was added to 200 ml. of a boehmitealumina and after contact for fifteen minutes, the unadsorbed liquid wasdecanted from the catalyst pellets. The resulting im- We claim:

1. A process for hydrodealkylating alkyl aromatic hydrocarbons in amixture comprising; contacting the hydrocarbon mixture with a catalystconsisting essentially pregnated catalyst was dried at 250F for one hourand 5 of about 5 to 15 percent of an active metal of Group calcined inair at 950F for sixteen hours in a muffle VIB of the Periodic System andabout 1 to percent furnace. This yielded a catalyst of the followingcompoby weight of a promoter metal selected from the group SitiOn:consisting of rubidium, cesium, calcium, strontium,

barium, and thorium, and mixtures thereof, both im- 10 percent Cr2o3 4percent CS2O A12O3 10 pregnated on an alumina carrier selected from thegroup consisting of boehmite, bayerite, beta, alumina- Example magnesia,and mixtures thereof, under conditions suffi- To 500 ml. of distilledwater was added 41 g. of cecient to effect said hydrodealkylationreaction, includrous nitrate hexahydrate and 100 g. of chromic nitrate.ing a temperature of about l,050 to l,200F., a pres- This solution wasadded to 500 ml. of a bayerite alusure of about 100-],000 psig., aliquid hourly space vemina and after contact for fifteen minutes, theunadlocity of about 0.1 to 5.0 and a hydrogen-tosorbed liquid wasdecanted from the catalyst pellets. hydrocarbon mole ratio between about3 and 15 to l. The resulting impregnated catalyst was dried at 250F 2. Aprocess in accordance with claim 1 wherein the for one hour and calcinedin air at 950F in a muffle promoter metal is calcium. furnace for 16hours. This yielded a catalyst of the fol- 20 3. A process in accordancewith claim 1 wherein the lowing composition: promoter metal isstrontium.

. 4. A process in accordance with claim 1 wherein the 10 percent Cr O -2percent Ce O Al O promoter metal is ri m- 5. A process in accordancewith claim 1 wherein the The following Table illustrates the advantagesof the promoter metal is thorium. catalysts of the present invention ascompared with a 6. A process in accordance with claim 1 wherein thecommerical chromia-magnesia on alumina catalyst. promoter metal isrubidium.

TABLE 1 [Feed: toluene. Standard conditions: l,150 F., 500 psig., 0.5LHSV, .3/1 lIz/II'C] Run Catalyst 12 (Jr-2 Mil-A1203 10 Cr-t K-Al O; wCr-lCs-AlgO; 12 cm C0-Al20 12 cm tit-A1203 Liquid recovery volumepercent feed 8-1 83 80 77.0 83. U Product distribution Benzene. U. 8 0.7 I), u 1. l o. 3 Benzene... 66.8 75.6 81.5 80.0 71.8 Toluene s2. 4 23.111. 3 13. s 38.0 Weight percent feed:

Toluene conversion 72. 8 80. 2 86. 2 80. 4 To. Selectivity to benzene 9293 {)2 8!! -94 Carbon on catalyst; weight percent iced 0.- 0. 1!) 0. 07.005 .005

7. A process in accordance with claim 1 wherein the promoter metal iscesium.

8. A process in accordance with claim 1 wherein the alumina carrier is agamma alumina.

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2. A process in accordance with claim 1 wherein the promoter metal iscalcium.
 3. A process in accordance with claim 1 wherein the promotermetal is strontium.
 4. A process in accordance with claim 1 wherein thepromoter metal is barium.
 5. A process in accordance with claim 1wherein the promoter metal is thorium.
 6. A process in accordance withclaim 1 wherein the promoter metal is rubidium.
 7. A process inaccordance with claim 1 wherein the promoter metal is cesium.
 8. Aprocess in accordance with claim 1 wherein the alumina carrier is agamma alumina.